Screw extruders are machines in which material such as polymers, elastomers, etc. are processed and then the extruded material is processed by a plurality of dies to form the required product. A typical screw extruder comprises at least one extruder screw shaft where each of the extruder screw shafts has a set of extruder screw elements mounted on them. The extruder screw shafts along with extruder screw elements are housed in a barrel. The barrel comprises multiple barrel sections which are joined end to end. Multiple barrel sections are required to carry out different processes involved in extrusion such as conveying, kneading, mixing, devolatilizing, metering and the like. Each barrel section comprises a liner which is press fit into a barrel casing, and heating and cooling elements are provided to regulate temperature of barrel section within permissible range.
During the process of extrusion, the surface of the liner is subject to intensive abrading action. Due to this, the liner undergoes continuous wear. Hence, for proper extrusion process, the liner has to be replaced after a certain period of time. Since the liner is press fit into the barrel casing, the conventional barrel, sections make the replacement of the liner a cumbersome process.
Further, the conventional extruders have cooling channels drilled in the barrel casing with metal plates welded at the ends of the barrel casing to form a closed water cooling circuit. The temperature across the barrel section is regulated by circulating coolant such as water through the cooling channels. The water circulated in the cooling channels absorbs the externally transferred heat and the heat generated from the processing of the material, and evaporates leaving behind scales of salts on the surface of the cooling channels. Due to the formation of these scales, the inner surface of the cooling channels needs to be cleaned regularly. The conventional extruders require the welding plates to be removed from the ends of the barrel casing for cleaning purposes, which is a cumbersome process and may also result in damage to the liner.
The existing barrel sections further fail to ensure uniform temperature across the inner surface of liner. Due to this, consistency in the mechanical properties of the extruded material may be affected. A significant disadvantage of the current art is that parts that are not at the process temperature are clamped together, causing stresses in the extruder barrel.
In light of the above limitations, there is a need for a barrel casing for barrel sections in the screw extruder that enables easy replacement of liner, enables easy cleaning of cooling channels and maintains uniform temperature at the inner surface of the liner.